[runtime] Introduce maps for the likely cases of FromPropertyDescriptor.

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index d372494250ab6ccc26f0a2b7798c8eef6323b9fc..af97787b7f3d184c6a0e2daac9a98cb77d85393d 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -2728,6 +2728,89 @@ bool Genesis::InstallNatives(ContextType context_type) {
 
   InstallBuiltinFunctionIds();
 
+  // Create a map for accessor property descriptors (a variant of JSObject
+  // that predefines four properties get, set, configurable and enumerable).
+  {
+    // AccessorPropertyDescriptor initial map.
+    Handle<Map> map =
+        factory()->NewMap(JS_OBJECT_TYPE, JSAccessorPropertyDescriptor::kSize);
+    // Create the descriptor array for the property descriptor object.
+    Map::EnsureDescriptorSlack(map, 4);
+
+    {  // get
+      DataDescriptor d(factory()->get_string(),
+                       JSAccessorPropertyDescriptor::kGetIndex, NONE,
+                       Representation::Tagged());
+      map->AppendDescriptor(&d);
+    }
+    {  // set
+      DataDescriptor d(factory()->set_string(),
+                       JSAccessorPropertyDescriptor::kSetIndex, NONE,
+                       Representation::Tagged());
+      map->AppendDescriptor(&d);
+    }
+    {  // enumerable
+      DataDescriptor d(factory()->enumerable_string(),
+                       JSAccessorPropertyDescriptor::kEnumerableIndex, NONE,
+                       Representation::Tagged());
+      map->AppendDescriptor(&d);
+    }
+    {  // configurable
+      DataDescriptor d(factory()->configurable_string(),
+                       JSAccessorPropertyDescriptor::kConfigurableIndex, NONE,
+                       Representation::Tagged());
+      map->AppendDescriptor(&d);
+    }
+
+    Map::SetPrototype(map, isolate()->initial_object_prototype());
+    map->SetInObjectProperties(4);
+    map->set_unused_property_fields(0);
+
+    native_context()->set_accessor_property_descriptor_map(*map);
+  }
+
+  // Create a map for data property descriptors (a variant of JSObject
+  // that predefines four properties value, writable, configurable and
+  // enumerable).
+  {
+    // DataPropertyDescriptor initial map.
+    Handle<Map> map =
+        factory()->NewMap(JS_OBJECT_TYPE, JSDataPropertyDescriptor::kSize);
+    // Create the descriptor array for the property descriptor object.
+    Map::EnsureDescriptorSlack(map, 4);
+
+    {  // value
+      DataDescriptor d(factory()->value_string(),
+                       JSDataPropertyDescriptor::kValueIndex, NONE,
+                       Representation::Tagged());
+      map->AppendDescriptor(&d);
+    }
+    {  // writable
+      DataDescriptor d(factory()->writable_string(),
+                       JSDataPropertyDescriptor::kWritableIndex, NONE,
+                       Representation::Tagged());
+      map->AppendDescriptor(&d);
+    }
+    {  // enumerable
+      DataDescriptor d(factory()->enumerable_string(),
+                       JSDataPropertyDescriptor::kEnumerableIndex, NONE,
+                       Representation::Tagged());
+      map->AppendDescriptor(&d);
+    }
+    {  // configurable
+      DataDescriptor d(factory()->configurable_string(),
+                       JSDataPropertyDescriptor::kConfigurableIndex, NONE,
+                       Representation::Tagged());
+      map->AppendDescriptor(&d);
+    }
+
+    Map::SetPrototype(map, isolate()->initial_object_prototype());
+    map->SetInObjectProperties(4);
+    map->set_unused_property_fields(0);
+
+    native_context()->set_data_property_descriptor_map(*map);
+  }
+
   // Create a constructor for RegExp results (a variant of Array that
   // predefines the two properties index and match).
   {